Method and apparatus for quantitative analysis using terahertz radiation

Abstract

A method of quantitatively analysing a sample, the method comprising: irradiating the sample with radiation having a plurality of frequencies in the range from 25 GHz to 100 THz; detecting radiation reflected from and/or transmitted by said sample to obtain a frequency domain waveform of said sample; identifying at least one section of interest of said frequency domain wave-form containing spectral features due to intermolecular or other non-intramolecular excitations; and obtaining a value related to the concentration of a component of the sample from the said section.

1. A method of quantitatively analysing a sample, the method comprising:
 irradiating the sample with radiation having a plurality of frequencies in the range from 25 GHz to 100 THz; 
 detecting radiation reflected from and/or transmitted by said sample to obtain a frequency domain waveform of said sample; 
 identifying and selecting at least one section of interest of said frequency domain waveform containing spectral features due to intermolecular or other non-intramolecular excitations, wherein the sample has components which are not to be analysed and the at least one section of interest is selected away from strong spectral features which arise from said components not to be analysed; and 
 determining the concentration of a component of the sample from the at least one selected section of interest. 
 
     
     
       2. A method according to  claim 1 , wherein the sample comprises a molecule which can form at least two polymorphs or psuedo polymorphic states. 
     
     
       3. A method according to  claim 2 , wherein regions of the spectra where there are differences between the characteristic spectra of the at least two polymorphs or psuedo polymorphic states are identified as sections of interest. 
     
     
       4. A method according to  claim 1 , wherein said sample comprises two or more components comprising different molecules. 
     
     
       5. A method according to  claim 1 , wherein the sample comprises an active component and an excipient. 
     
     
       6. A method according to  claim 1 , wherein the sample comprises solid components. 
     
     
       7. A method according to  claim 1 , wherein the sample comprises a pharmaceutical. 
     
     
       8. A method according to  claim 1 , wherein the sample comprises explosive materials. 
     
     
       9. A method according to  claim 1 , wherein the sample comprises at least one component in the form of a vapour. 
     
     
       10. A method according to  claim 9 , wherein the vapour is water vapour. 
     
     
       11. A method according to  claim 9 , wherein the section of interest is chosen as a region of the spectra which contains features arising from rotational excitations of the molecules which comprise the vapour. 
     
     
       12. A method according to  claim 1 , wherein the sample comprises a sealed package. 
     
     
       13. A method according to  claim 12 , wherein radiation transmitted by or reflected from the headspace of the package is analysed to determine the vapour content in the package. 
     
     
       14. A method according to  claim 1 , wherein the sample is analysed through packaging. 
     
     
       15. A method according to  claim 1 , wherein the sample is irradiated with radiation in the range from 100 GHz to 5 THz. 
     
     
       16. A method according to  claim 1 , wherein obtaining a value related to the concentration of the component comprises obtaining a derivative of said section. 
     
     
       17. A method according to  claim 16 , wherein said derivative is the first derivative. 
     
     
       18. A method according to  claim 16 , wherein said derivative is the second derivative. 
     
     
       19. A method according to  claim 1 , wherein said step of obtaining a value related to the concentration of a component comprises subtracting a background signal from said detected radiation. 
     
     
       20. A method according to  claim 19 , wherein said step of subtracting a background signal comprises detecting the radiation reflected from or transmitted by a reference sample placed in the position of the said sample. 
     
     
       21. A method according to  claim 19 , wherein said step of subtracting a base line signal comprises fitting a straight line to the spectra and subtracting it from said spectra. 
     
     
       22. An apparatus for quantitatively analysing a sample, comprising:
 a source for irradiating the sample with radiation having a plurality of frequencies in the range from 25 GHz to 100 THz; 
 a detector for detecting radiation reflected from and/or transmitted by said sample to obtain a frequency domain waveform of said sample; 
 means for identifying and selecting at least one section of interest of said frequency domain waveform containing spectral features due to intermolecular or other non-intramolecular excitations; and 
 means for determining the concentration of one polymorph of a component of the sample relative to the amount of another polymorph or pseudo polymorph of said component from the at least one selected section of interest. 
 
     
     
       23. An apparatus according to  claim 22 , wherein the source is a pulsed source of radiation. 
     
     
       24. An apparatus according to  claim 22 , wherein the source is a source of continuous wave radiation. 
     
     
       25. An apparatus according to  claim 22 , wherein the source comprises an optically non-linear member which is configured to output radiation in the desired frequency range in response to irradiation by radiation having two or more different frequencies. 
     
     
       26. An apparatus according to  claim 22 , wherein the source is comprises a photoconductive antenna which is configured to output radiation in response to a bias applied across the antenna and irradiation by radiation having two or more different frequencies. 
     
     
       27. An apparatus according to  claim 22 , wherein the source is configured to output radiation in the range from 100 GHz to 5 THz. 
     
     
       28. An apparatus according to  claim 22 , wherein the detector is configured to detect radiation using electrooptic sampling. 
     
     
       29. An apparatus according to  claim 22 , wherein the detector comprises a photoconductive antenna.